The present invention refers to a procedure and an installation for on-site manufacturing of explosives by means of incorporating fuel and gas into an oxidant water based product with formation of emulsion or dispersion of the fuel and the gas in the liquid mixture.
The initiation mechanism of explosives by means of generation of hot points due to the adiabatic compression of gas bubbles is the basis of modern industrial explosives formulated without components that are intrinsically explosive.
The introduction of gas bubbles can be done either by entrapment during the mixture or by its formation by means of a chemical reaction. U.S. Pat. No. 3,400,026 describes a formulation that employs protein in dissolution (albumin, collagen, soy protein, etc.) to favor the formation of bubbles and their stabilization. U.S. Pat. No. 3,582,411 describes a formulation of explosive hydrogel that contains a foam promoting agent of the guar gum type modified with hydroxyl groups.
U.S. Pat. No. 3,678,140 describes a process for the incorporation of air by means of the use of protein solutions, making the composition pass through a series of openings at pressures of 40 to 160 psi and simultaneously introducing air by means of eductors.
The incorporation of gas bubbles by means of their generation as a result of a chemical reaction is described in U.S. Pat. Nos. 3,706,607, 3,711,345, 3,713,919, 3,770,522, 3,790,415 and 3,886,010.
Regarding the on-site manufacture of explosives, that is, in the truck itself which is used for pumping the explosives into the bores, the first patents are from IRECO, as described in U.S. Pat. Nos. 3,303,738 and 3,338,033. These patents are characterized by the manufacturing in the truck of an explosive of the hydrogel type by means of the dosing and mixture of a liquid solution of oxidizing salts with a solid material that contains oxidizing salts and thickeners. In U.S. Pat. No. 3,610,088 (IRECO) they use the same method as the previous patents for the on-site forming of the hydrogel and they incorporate the simultaneous addition of air either by means of mechanical entrapment or their generation by means of a chemical reaction. EP Patent 0 203 230 (IRECO) describes a mixer consisting of moveable and fixed blades which allow an on-site manufacturing of a blasting agent of the water emulsion in oil type. The sensitization of this emulsion is accomplished by adding low density particles (oxidants or hollow microspheres).
The on-site manufacturing of the explosive has as its main advantage a decrease of risk during its transportation. However, it is necessary to have a very sophisticated mobile installation with complex processes for manufacturing and control, due to the use of oxidizing salts at high temperatures, dosing of solids and mixtures of liquids and solids.
Another alternative is the transportation of the finished product without sufficient sensitizing, that is, at a density such that it does not have the capacity to propagate a stable detonation. In this context in recent years it has become common to transport the matrix product and produce its sensitization at the mine either by means of mixing it with low density particulated nitrates or mixtures of ammonium nitrate with hydrocarbide (ANFO) or by means of the generation of bubbles from a chemical reaction. U.S. Pat. No. 4,555,278 describes an explosive of this type manufactured by a mixture of emulsion and ANFO. European Patent EP 0 194 775 describes an explosive of the previous type, made from a hydrogel matrix.
The sensitization of the matrix emulsion by means of gas bubble generation from a chemical reaction is presently the most widespread method. However, to avoid the coalescence of the gas bubbles, as described in U.S. Pat. No. 4,008,108, the pumping and the manipulation of the emulsion must be performed before the gasification reaction occurs. This method thus presents the disadvantage of having to wait a certain amount of time after filling the bores until reaching the final density, not having the capacity to maneuver if the obtained density does not coincide with what is expected, possibly causing sensitization failures or an incorrect dispersion of explosive in the bore column.
Patent application WO 99/00342, in the name of UNIÓN ESPAÑOLA DE EXPLOSIVOS, S.A., claims a process for the sensitizing of water based explosives before loading the bores, from a non-explosive matrix consisting of oxidants and fuels, by means of the formation of an emulsion or dispersion of gas in said matrix. The density control is performed before loading the bore, regulating the flow of gas that is injected.
Although the transport of a matrix product and its on-site sensitization supposes a large advance from the safety point of view compared to the transportation of the already sensitized product, there are various experiences of accidents in which a detonation of a non-sensitized matrix product has occurred as a consequence of an inadequate manipulation or by the effect of a prolonged fire. For this reason, in some countries, such as Australia, a new denomination has been created for matrices of mixtures of oxidants and reductants known as explosive precursors. Although these types of products are classified for transportation as oxidants 5.1, they must be manufactured in facilities that have the safety measures, distances, etc., of an explosive manufacturing plant.
The present invention eliminates the transportation of explosives or mixtures of oxidants and reductants commonly known as matrices or explosive precursors, by means of the on-site manufacture of the explosive, that is, at the place of use, without the inconveniences that this process presented until now (complex installations, difficult handling of intermediary products, complex processes, etc.). The invention consists of the manufacture within the industrial area of a suspension of oxidizing salts in a water solution saturated with oxidizing salts, stabilized by means of a thickener preferably of inorganic origin that will allow to maintain the oxidant particles dispersed in a homogenized manner. In the event of using organic thickeners, the percentage of it is sufficiently small so that said suspension may be considered as an oxidant suspension.
According to the present invention, the manufacture and sensitization of the explosive is performed on-site, by means of an intimate mixture of said stable oxidant dispersion at room temperature, with a fuel and a gas in a mixer, causing the formation of a suspension or emulsion of gas in liquid. The density of the end explosive product may be varied as a function of the volume of gas and this is controlled before introducing it into the bore.